In a radio communication system, e.g. in the Global System for Mobile Communication (GSM), communications are built up between a base station and a number of mobile stations. The mobile stations are used by users and may change their geographical location due to movements of the users. The base station is operated by a provider who offers location-based services to the users. Such services may comprise e.g. location dependent weather forecasts and the like.
For these location-based services, it is necessary that the provider knows the geographical location of the respective user. For that purpose, at least three methods are known to evaluate the geographical location.
In a first method, the fact is used that the geographical area covered by the provider is partitioned into cells and that each cell carries a particular identification. This identification is used as a geographical information. The identification is available for the respective mobile station as well as for the base station and may therefore be used by the location-based service. This first method is inexpensive but not very accurate.
A second method is based on the first method and comprises the following additions. E.g. the signal strength of the radio signal being transmitted from the mobile station to the base station is measured. With this information, it is possible to estimate the distance of the mobile station from the base station. Similar measurements and evaluations may be carried out depending on the propagation time of a signal e.g. from the base station to the mobile station and back. The estimated distance is then used in addition to the cell identification as a geographical information. This second method requires additional steps to be carried out and therefore additional costs compared to the first method. However, it is more accurate than the first method.
In a third method, the Global Positioning System (GPS) is used. For that purpose, a GPS receiver for receiving GPS signals has to be present in the mobile station. The geographical information of the received GPS signals may then be used by the location-based service. Of course, this third method is most accurate but also most expensive.
It is an object of the invention to provide a method for evaluating geographical information of the location of the mobile station with high accuracy without requiring high additional costs.